This invention relates to wireless communications systems and, more particularly, to wireless communications between wireless terminals and base stations in a multiple access communications system.
Typically, the wireless channel used in a wireless communications system is not as reliable as a wireline channel, because of such channel impairments as multipath fading and Doppler spread. One general technique of improving the wireless channel reliability is to use automatic repeat requests (ARQs). That is, if a received traffic data is detected as having errors, the transmitter will be instructed to retransmit the same traffic data again. When the wireless channel condition and/or interference condition is not completely correlated, retransmission increases the probability of successful traffic reception. One such wireless communications system is the Orthogonal Frequency Division Multiplexing (OFDM) based Spread Spectrum Multiple Access system.
In prior known wireless systems, ARQ is based on exchanging control messages. Specifically, when the receiver detects an error in the received traffic data, it transmits back a control message that includes a request for retransmission of the erroneous traffic data in a control channel dedicated between the transmitter and the receiver. In general, the retransmission request contains the identifier of a corrupted or missed traffic data, such as its sequence number.
Additionally, because the dedicated control channel is also used to convey other control messages, the retransmission request message may have to be inserted into a generic control message format, which may include a greater number of bits than is required by the retransmission request message. Moreover, a specific control message header is typically included for the retransmission request message. Hence, the control message based transmission technique of retransmission requests may take a long time to transmit and cause large overhead, which s very undesirable. As a result, it is generally considered that real-time traffic cannot benefit much from ARQ as the transmission of the retransmission request is not fast enough to meet system deadline requirement.
These and other problems and limitations of prior known wireless communications system traffic data retransmission arrangements are overcome by managing the channel resource by utilizing traffic segments and acknowledgment segments. This is realized by partitioning the channel resource into an acknowledgment channel and a traffic channel in a fixed manner. The acknowledgment channel includes acknowledgment segments and the traffic channel includes traffic segments. A traffic segment is the basic resource unit to transport traffic data and has a prescribed finite time interval and bandwidth.
Specifically, each traffic segment in the downlink or uplink is associated with an acknowledgment segment in the uplink or downlink, respectively, in a prescribed one-to-one manner. The acknowledgment segment is used to convey the acknowledgment information of the associated traffic segment. When traffic segments are used by different users, the associated acknowledgment segments are also used by different users.
The base station uses the acknowledgment segments in the downlink to acknowledge the associated traffic segments received in the uplink. A wireless terminal that receives a downlink traffic segment uses the associated acknowledgment segment in the uplink to acknowledge the traffic segment. The base station monitors all the acknowledgment segments associated with the traffic segments that the base station has transmitted to determine whether any of the traffic segments needs to be retransmitted. When a wireless terminal has transmitted a traffic segment in the uplink, it monitors the associated acknowledgment segment in the downlink to determine whether the traffic segment needs to be retransmitted.
Advantageously, given the prescribed association, the acknowledgment segment does not specify the resource parameters of the traffic segment, i.e., the slot and waveform set indices, or the identifier of the missed traffic data, such as sequence number. Instead, the essential information to be contained in an acknowledgment segment is just one-bit of information indicating whether the associated traffic has been successfully received. In addition, to facilitate other physical layer functions such as for the transmitter to measure the channel quality, an acknowledgment segment may also include some information of decoding results for the associated traffic segment, such as a measure of the raw error rate.